Exercise responsive pacemaker tuning method using Doppler blood flow measurements to adjust pacing for optimized flow

ABSTRACT

A method of tuning a cardiac prosthetic pacing device includes (a) monitoring the flow output from the heart, and (b) adjusting the timing of pacing events by the cardiac prosthetic pacing device so as to optimise the flow from the heart under operational conditions.

FIELD OF THE INVENTION

The present invention relates to the field of cardiac pacemakers and, inparticular, discloses a methodology and apparatus for selectively tuninga pacemaker-type device.

BACKGROUND OF THE INVENTION

Pacemaker devices normally consist of the pacemaker control unitcontaining a power cell such as a battery, a pacemaker lead and endelectrodes which are attached to the heart so as to stimulate the heartinto action at certain timed occurrences. Recent advances in pacemakertechnology include providing for fully programmable capabilities. Modernpacemaker devices such as those available from Medtronic Inc ofteninclude on board processing and storage capabilities and the latestmodels allow for external communication with reader and control deviceslocated outside the body for telecommunications. Examples of suchsystems are disclosed in U.S. Pat. No. 6,577,901 to Thompson, U.S. Pat.No. 6,580,946 to Struble and U.S. Patent Application 2003/0100925 toPape et al. the contents of each of which is incorporated by crossreference disclose suitable forms of heart pacemaker technology suitablefor us with the present invention.

As is disclosed in the aforementioned patents, modern pacemaker devicesalso allow for a variability in operation of the heart in accordancewith external needs. For example, during exercise, the pacemaker devicemay increase the heart rate. Further, during periods of rest, thepacemaker device may decrease the heart rate. Further, programmablepacemakers allow for storage of information for downloading as to theonboard operation of the pacemaker unit.

There is therefore a general need to accurately and succinctly tune thepacemaker unit for the proper operation of the heart muscle.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide for a method andapparatus for tuning the operation of pacemaker units to achieve moreoptimal results.

In accordance with a first aspect of the present invention, there isprovided a method of tuning a cardiac prosthetic pacing device, themethod comprising the steps of (a) monitoring the flow output from theheart; and (b) adjusting the timing of pacing events by the cardiacprosthetic pacing device so as to optimise the flow from the heart underoperational conditions.

Preferably, the method includes monitoring the flow utilising acontinuous wave Doppler signal directed at the heart. Ideally, themethod is repeated under a number of different operational conditionsfor a patient including walking and/or running. Further, preferably themethod is repeated under a number of different pharmalogical conditionsfor a patient.

In accordance with a further aspect of the present invention, there isprovided an apparatus for tuning a cardiac prosthetic pacing device, theapparatus including: monitoring means for non invasively monitoring theflow of blood out of the heart; control means for controlling theoperation of the cardiac prosthetic pacing device including variation ofthe pacing rate; and processing means interconnected to the monitoringmeans and the control means, the processing means instructing thecontrol means to vary the pacing rate of the cardiac prosthetic pacingdevice and monitor the corresponding measurement of the monitoringmeans.

Preferably, the monitoring means includes a continuous wave Dopplersensor device for emitting and receiving a CW-Doppler signal directedand reflected from the patient's heart.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 illustrates a first operational environment of the preferredembodiment;

FIG. 2 illustrates a sectional view through a transducer device;

FIG. 3 illustrates a velocity time snapshot as measured by the CWtransducer device;

FIG. 4 illustrates various portions of the snapshot of FIG. 3;

FIG. 5 and FIG. 6 illustrates flowcharts of the steps involved inoptimising the pacemaker arrangement of the preferred embodiment.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment, continuous wave ultrasound techniques areutilised to transcutaneously measure the cardiac output of a heartoperating with a cardiac prosthetic pacing device. Through utilisationof ultrasound techniques, a measurement of cardiac output can beobtained as a function of rate and volume. The ultrasound techniquesalso provide a measure of stroke volume thereby providing informationfor optimisation of settings of the pacemakers.

Turning initially to FIG. 1, there is illustrated one arrangementutilising the preferred embodiment. In this arrangement, a patient 10has attached two non-invasive monitoring devices 11-13. Each of the twodevices 11-13 are interconnected to aprocessing and display unit eg. 12,14. Each of the units 12, 14 includes an internal computer processingmeans, a display and a series of control buttons for controlling thefunctionality of the device. Each of the devices 12, 14 are furthernetworked to a base station or the like for overall monitoring andcontrol.

The sensor 13 is in telemetry connection with the heart pacemaker unit.It is assumed that the device 14 in conjunction with sensor 13 is ableto vary the rate at which the heart paces. Such systems are disclosed inthe aforementioned patent applications.

Hence, variations in blood flow around the body can be measured byalteration of the heart pacemaker timing period whilst simultaneouslymonitoring the corresponding alteration in blood flows as detected bythe CW transducer device. In this manner the pacing period can beoptimised for the particular recipient by estimation of the flowrequirements of the recipient given their size, weight etc.

FIG. 2 shows an example of the first actuator 11 for attachment to theskin surface. Ideally CW Doppler is utilised to monitor the blood flowwithin the heart. CW Doppler is a non-invasive technique in whichultrasonic signals from transducer elements are directed into a bloodcarrying vessel of a patient. Doppler shifts in the reflected signalprovide an indication of the rate of blood flow. In FIG. 2, a transducerelement 11 includes an ultrasonic transducer 15 attached to apositioning device 16 which can be used to initially set the position ofthe transducer. Between the transducer 15 and a patient's skin 17 isplaced a gel coupling layer 18 for coupling the ultrasonic transducervibrations to the skin 17. The principles of CW Doppler flow measurementare known. Patent Cooperation Treaty (PCT) publication number WO99/66835 to the present assignee, the contents of which are incorporatedherein by cross-reference, describes in more detail an ultrasonictransducer device suitable for measuring blood flow using the CW Dopplermethod.

In the embodiment shown in FIG. 1, the transducer elements are placed onthe patient to obtain intra-cardiac or aortic signals, for examplethrough a suprasternal notch.

The CW method detects the velocity of individual blood cells bymeasuring the frequency change of a reflected ultrasound beam anddisplaying this as a velocity time flow profile, an example of which isshown in FIG. 3. The transducer output forms an input to the processorunit which image processes the results of FIG. 3 so as to calculate fromthe velocity time flow profile, the velocity time integral (tvi) andother relevant information such as heart rate (HR) and peak volume Vpk.These calculations can then be compared with the pacemaker timingsetting to determine an overall optimal performance.

The arrangement of FIG. 1 can then be translated into other real lifesituations. For example with the patient on a walking treadmill and arunning treadmill. Again, measurements can be taken of variation inblood flow pumping rates with variation in heart rates so as to therebytune the operation of the pacemaker unit for the particular individualto particular activities. These results can then be stored in thepacemaker unit for future use.

A flow chart of the overall steps involved in the operation of thepreferred embodiment is illustrated generally 30 in FIG. 5. Theseinclude the steps of obtaining a CW Doppler flow measurement 31 andsimultaneously obtaining pacemaker rate measurements 32. Next, adetermination is made as to whether to increase or decrease thepacemaker rate measurement 33. Upon increasing or decreasingmeasurements, continual analysis of the change in flow rate is made 34.

Through the utilisation of flow measurements via the CW technique,advanced analysis can also be conducted in a more non invasive manner.Normally, pacemakers are designed to regulate cardiac output bycontrolling the timing of events in the cardiac cycle and are usuallyset according to ECG criteria. ECG devices however measure only theheart rate and make no measure of cardiac output, a function of rate andvolume, which is a measure of how much the heart pumps. The CW methodprovides a measure of the heart rate and total volume the heart pumpsthereby providing more information required for optimisation of thesettings of pacemaker devices. Obviously, testing in accordance with awide variety of physiologic (exercise) conditions or pharmacologictesting is desirable.

Modern pacing devices are conceived to optimise cardiac performance.Cardiac performance is a function of rate and output volume. Currentmethods for setting parameters are generally based on rate setting froman ECG. The ultrasound device 12 provides both rate and volumeinformation so that pacemaker timing of cardiac events can be optimised.In particular, biventricular pacing devices allow asynchronousactivation of ventricular chambers. Indeed, the delay period between theactivation of right and left ventricular chambers effect the optimalhaemodynamic performance and varies with individual physiology andpathophysiology.

The use of the transcutaneous sensing of blood flow within the heartallows for the determination of optimal pacing delays in pacemakerdevices leading to more appropriate use and effect of these devices.

Further, By carrying out a large number of tests on a large number ofpatients under a large number of different conditions, various indiciescan be built up in guiding the system in setting the pacing rates forparticular patient activities. The test can be carried out on aplurality of patients and the total set of results statisticallycombined, e.g. averaged for patient variables such as age, sex, weightetc.

Upon conducting an analysis of flow rate with activity type, adetermination can be made of the desirable flow rate for standardactivity types measurable with the type of pacemaker device utilised.The desirable flow rate for each activity type can then be uploaded tothe pacemaker device and utilised to tune the pacemaker's operation. Forexample, FIG. 6 illustrates a flow chart of one possible control loopwithin the pacemaker device. Utilising a precalculated stored table ofcorrespondence between rate type and activity type 63, a given currentactivity type is input 63. The difference between a current rate and theactivity type rate is calculated 61 and the current rate is slowlychanged so that it is closer to the current activity rate. The systemcan operate in a feedback loop constantly with a predetermined delay 62.

Additionally, the invention as described herein can be used to improveunderstanding of the normal physiology and pathophysiology associatedwith cardiovascular function, exercise and pulmonary function.

It will be understood that the invention disclosed and defined hereinextends to all alternative combinations of two or more of the individualfeatures mentioned or evident from the text or drawings. All of thesedifferent combinations constitute various alternative aspects of theinvention.

The foregoing describes embodiments of the present invention andmodifications, obvious to those skilled in the art can be made thereto,without departing from the scope of the present invention.

1. A method of tuning a cardiac prosthetic pacing device, the methodcomprising the steps of: (a) monitoring the flow output from the heartutilizing a transcutaneous continuous wave Doppler signal directed atthe heart to obtain a signal indicative of intra-cardiac blood flowvelocity under a number of different operation conditions for a patientincluding walking and running; (b) constructing a table ofcorrespondence between activity type and flow rate and storing saidtable on said cardiac prosthetic pacing device; and (c) using saidtable, adjusting the timing of pacing events by said cardiac prostheticpacing device so as to optimise the flow from the heart underoperational conditions.
 2. A method as claimed in claim 1 wherein saidmonitoring is repeated under a number of different pharmalogicalconditions for a patient.
 3. A method as claimed in claim 1 wherein saidmonitoring is conducted on a number of patients.
 4. A method as claimedin claim 3 wherein results from the number of patients are statisticallycombined.
 5. A method as claimed in claim 4 wherein the statisticalcombination of results includes averaging for at least one of age, sexand weight.
 6. A method as claimed in claim 1 wherein the adjustment ofthe timing of pacing events includes calculating a difference between acurrent rate and an activity rate obtained from said table and adjustingthe timing of pacing events so that the current rate is closer to theactivity rate.
 7. A method as claimed in claim 6 wherein said adjustmentoperates in a feedback loop constantly with a predetermined delay.